Date of death from administrative data. This variable is obtained using a hierarchy of administrative sources: (i) SSA's MBR file, (ii) SSA's SSR file, and (iii) the Census PCF with death information coming from the SSA Numident and Master Death Files. This variable is coded as a SAS date variable. This format gives the number of days between the date of birth and January 1, 1960. An individual born on January 1, 1959 would have birthdate=-365 and an individual born on January 1, 1961 would have birthdate=365.